Universal serial bus selective encryption

ABSTRACT

A method to interact with a remote USB device is disclosed. An identifying message is received from a remote client associated with the remote USB device. The remote USB device is identified based at least in part on the identifying message from the remote client. A security policy is determined for the remote USB device. A policy message is transmitted to the remote client for selectively implementing the security policy of the remote USB device. A method to interact with a local USB device is disclosed. An identifying message is determined by performing a host controller service for the local USB device. The identifying message is transmitted to a server. A policy message is received from the server for selectively implementing a security policy on the local USB device. The security policy is regarded and configuring the host controller service.

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 60/997,842 entitled UNIVERSAL SERIAL BUS ACROSS A NETWORK filed Oct. 5, 2007 which is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

The Universal Serial Bus (“USB”) standard is a popular bus standard for connecting devices. USB is popular in part because a large selection of devices use it including servers, clients, serial devices, parallel devices, keyboards, mice, language devices, pointing devices, human input devices, video devices, audio devices, printers, scanners, network adapters and voice-over-Internet-Protocol (“VoIP”) devices.

Thin clients can provide efficient use of compute resources across multiple users and multiple locations. A thin client is made more useful by allowing USB devices to connect to it. However, sensitive information including user names and user passwords may be transmitted using these USB devices. It would be useful to protect this sensitive information.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.

FIG. 1 is a block diagram illustrating an embodiment of a system for USB over a thin network.

FIG. 2A is a block diagram illustrating an embodiment of a USB system architecture for a thin client.

FIG. 2B is a block diagram illustrating an embodiment of a USB system architecture for a server.

FIG. 3 is a flow chart illustrating an embodiment of a process for USB over a thin network.

FIG. 4 is a flow chart illustrating an embodiment of a process for initializing a USB host controller.

FIG. 5 is a flow chart illustrating an embodiment of a process for processing USB devices using a hybrid USB stack.

FIG. 6 is a flow chart illustrating an embodiment of a process for processing USB language devices.

FIG. 7 is a flow chart illustrating an embodiment of a process for USB information extraction.

FIG. 8A and FIG. 8B are an example of a register map for an assistance engine and message analyzer.

FIG. 9 is a flow chart illustrating an embodiment of a process for USB selective encryption.

FIG. 10 is an example of a register map for a security engine.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as a process, an apparatus, a system, a composition of matter, a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or communication links. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. A component such as a processor or a memory described as being configured to perform a task includes both a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. As used herein, the term ‘processor’ refers to one or more devices, circuits, and/or processing cores configured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.

USB over a thin network, USB message extraction, and USB selective encryption are disclosed. Throughout this specification “thin network” refers to any network using a thin network protocol. Throughout this specification “hardware” refers to any physical configuration of digital circuits to perform a task, including custom silicon integrated circuits, application specific integrated circuits (“ASICs”), field programmable gate arrays (“FPGAs”) or programmable logic devices (“PLDs”). Throughout this specification an algorithm or method “practically implementable by hardware” refers to any algorithm or method that is directly, natively or practically realizable by hardware, such that the algorithm or method would completely fit on a single commercially available FPGA or PLD.

Throughout this specification a “driver level message” is a message that is practically implementable by hardware and is one or a combination of control and status register (“CSR”) reads, CSR writes, block data transfers, and interrupts. Throughout this specification a “thin client” is practically implementable by hardware and does not require an instruction based processing element, such as a central processing unit (“CPU”), microcontroller unit (“MCU”), or digital signal processor (“DSP”.)

In one embodiment a thin network protocol such as the Thinium Network Protocol (“TNP”) described in US Patent Pre-Grant Publication US-2008-0010340-A1 “THIN NETWORK PROTOCOL”, is used to tunnel driver level messages from a server to a thin client. In a thin network, to reduce costs or resources a thin client may be reduced in complexity such that it can be practically implementable by hardware. The thin client may include a USB host controller. However, because the thin client is practically implementable by hardware, the USB host controller driver may in some embodiments be executed on the server instead of the thin client.

FIG. 1 is a block diagram illustrating an embodiment of a system for USB over a thin network. In the example shown, server 102 is coupled to thin client 104. Thin client 104 communicates with USB device 106. In some embodiments server 102 and thin client 104 are connected directly through a local bus connection. In some embodiments server 102 and thin client 104 are connected through a network. Throughout this specification, “network” refers to any public or private network and/or combination thereof. A network may include the Internet, an Ethernet, a serial/parallel bus, intranet, local area network (“LAN”), wide area network (“WAN”), or any form of connecting multiple systems and/or groups of systems together. In some embodiments server 102 and thin client 104 are connected through a network by using a thin network protocol (“TNP”) over the Internet Protocol (“IP.”)

In various embodiments thin client 104 may communicate to USB device 106 using a USB protocol. Throughout this specification the “USB protocol” refers to one of either a wired USB protocol, for example:

-   -   USB 1.0;     -   USB 1.1;     -   USB 2.0;     -   USB 3.0; and     -   PoweredUSB,         or a wireless USB protocol, for example:     -   WirelessUSB;     -   Certified Wireless USB (“WUSB”);     -   Ultra-Wideband (“UWB”) USB radio platforms; and     -   Cable-Free USB.

FIG. 2A is a block diagram illustrating an embodiment of a USB system architecture for a thin client. In some embodiments, the architecture in FIG. 2A is the architecture for thin client 104. In FIG. 2A, optional blocks or systems are denoted by a grey fill and comprise assistance engine 208, message analyzer 210, hardware cursor 212 and security engine 214.

Thin client 202 comprises packet encoder and decoder 204 coupled with host controller 206. Packet encoder and decoder 204 is coupled directly or through a network to server 102. Host controller 206 may be a standard USB host controller coupled through the USB protocol to one or more USB devices 106. The packet encoder and decoder 204 and host controller 206 may also be coupled with the optional assistance engine 208. The assistance engine 208 may be coupled with the optional message analyzer 210, which may be coupled with the optional hardware cursor 212. The hardware cursor 212 is coupled to a Video Graphics Array (“VGA”) device such as a computer display monitor. The optional security engine 214 may be coupled with the packet encoder and decoder 204. Blocks 204, 208, 210, 212, and 214 may be implemented as separate subsystems or integrated onto a single FPGA or ASIC.

Packet encoder and decoder 204 is a tunneling agent which processes server packets and sends the encapsulated driver level messages to host controller 206. The agent is capable of returning data back to server 102. In the case where events such as interrupts need to be reported from the host controller 206 to the host controller driver, the packet encoder and decoder 204 sends a message back to server 102. An agent on the server side reports the event back to the USB host controller driver stack.

Assistance engine 208 provides a way to respond and resubmit transfer descriptors (“TDs”) to USB device 106 based at least in part on transfer descriptors received earlier. By using assistance engine 208, there is a substantial reduction in response time to an interrupt from the host controller 206; instead of using a processor which may not be able to respond to the assertion of the interrupt line immediately, the turnaround time for accessing the USB host controller is substantially smaller when using dedicated hardware 208. As well, eliminating the need to wait for server 102 to parse the TDs before access to the payload means that network traffic is substantially reduced if server 102 and client 104 are coupled via a network. Assistance engine 208 instead parses TDs on the fly when fetched and then encapsulate the payload immediately following the TD fetches for transmission to the server.

Message analyzer 210 increases the responsiveness of thin client 104 to USB device 106 to improve a user's experience. In some embodiments the message analyzer 210 is configured to parse USB device 106 as a pointing device. Throughout this specification “pointing device” refers to any input device that includes a cursor basis, including one or more of a: mouse, touchpad, pointing stick, trackball, light pen, touchscreen, graphics tablet, light gun, joystick, and dance pad. Throughout this specification “cursor” refers to both:

-   -   spatial data in one or more dimensions, for example, X-Y         coordinates on a two-dimensional plane, or Z-coordinates from a         scroll wheel; and     -   event data from one or more triggers, for example a button         click, double-click, drag, chording, or rocker.         Message analyzer 210 improves the responsiveness to a pointing         device by parsing cursor data from the pointing device at thin         client 104 instead of transferring each result of the pointing         device interrupt transfer to the server and then transmitting a         cursor update from server 102 to thin client 104.

Message analyzer 210 parses a subset of the data from the pointing device directly to reduce roundtrip network latency and reduces the user's perception that the pointing device is sluggish when used in conjunction with assistance engine 208. In some embodiments, message analyzer 210 parses a proper subset of the data from the pointing device, wherein throughout this specification a “proper subset” defines a portion of a given set of data that is strictly contained in the data, and thus there exists at least one element of data which is not contained in the portion. When the message analyzer 210 parses the data and positions the pointing device, response to a pointer device movement feels instantaneous. Cursor data is still sent to server 102, so that user interface elements can be rendered in response to pointing device movements as well as other software interactions with the pointer.

To accomplish pointing device processing with the message analyzer 210, server 102 must parse the initial USB Human Interface Device (“HID”) descriptors. Server 102 determines which offsets in the pointing device interrupt transfers contain spatial coordinate data, for example X and Y coordinate data. It also determines the range of these values. Server 102 configures thin client 104 by configuring assistance engine 208 and message analyzer 210 with these offsets and ranges. Server 102 also sets the initial pointer location and may update it from time-to-time in response to software requests.

Once assistance engine 208 is configured, it submits USB interrupt transfer requests to the pointing device 106. When the pointing device 106 moves and the message analyzer 210 receives the data from the interrupt transfer, it uses the configuration information received from server 102 to parse the data from the pointing device 106. In some embodiments, the position of hardware cursor 212 is then updated. Message analyzer 210 also sends a position update to server 102. The assistance engine 208 resubmits the interrupt transfer to handle additional pointer device position updates.

Hardware cursor 212 reflects cursor information canonically stored at server 102. Rendering a reflected pointer locally at thin client 104 improves a user's experience by enhancing the perception of responsiveness. The hardware cursor 212 comprise one or more of a:

-   -   pointer memory region to store the bitmap of the current pointer         representation for rendering. The current pointer representation         may include, for example, a bitmap of an arrow, hourglass, or         crosshair;     -   pointer block transfer command to copy data from a source region         to the pointer memory region for rendering. The pointer size and         stride may be variable or fixed;     -   set of registers indicating the screen extents including the         minimum and maximum coordinates of the usable pointer screen for         screen clipping and multi-monitor output; and     -   set of registers indicating the current pointer “hotspot”; the         singularity in space used to represent the cursor during events         like button clicks, within the bitmap of the current pointer.

Security engine 214 allows for selective security and encryption of USB for thin client 104. After an interrupt, the resulting TD and associated data are transferred from the client to the host. Security engine 214 enables this transfer to be secure or encrypted, and furthermore encryption may be selectively turned on or off. This allows only sensitive USB transfers to be encrypted, leaving non-sensitive transfers unencrypted, resulting in saving of compute power or electrical power. For example, a particular embodiment may consider that all mouse transactions are not sensitive and need not be encrypted, while transactions from another USB device may be encrypted.

In one embodiment, a security policy is selective encryption based on the type of TD. Encryption may use an appropriate key exchange algorithm such as RSA, and an appropriate encryption algorithm such as Advanced Encryption Standard (“AES”) to encrypt the data.

The memory space for host controller 206 is accessible from the server through the network stack. In some embodiments it is important to protect access via encryption. Security engine 214 facilitates a writable register to specify the base address that would require encryption. When a server accesses an address base larger or equal to the set address value in this register, the encryption out-of-band signal is asserted.

FIG. 2B is a block diagram illustrating an embodiment of a USB system architecture for a server. In some embodiments, the architecture in FIG. 2B is the architecture for server 102. In FIG. 2B, optional blocks or systems are denoted by a grey fill and comprise security engine 268.

Server 252 comprises packet encoder and decoder 254, which is coupled to host controller driver 256 and optional security engine 268. Host controller driver 256 is coupled with USB kernel driver 258, hub driver 260, language device driver 262, pointing device driver 264 and generic driver 266. In some embodiments USB kernel driver 258 is a kernel space component Throughout this specification, a “language device” refers to any language-based input device including one of a: keyboard, handwriting recognition pad, number pad, keypad, predictive language keypad, speech recognition device, and motion recognition device. Packet encoder and decoder 254 is coupled to thin client 104's packet and encoder and decoder 204 either directly or through a network. USB kernel driver 258 is coupled to the server's operating system (“OS”) stack.

Packet encoder and decoder 254 is a tunneling agent which processes client packets and sends the encapsulated driver level messages to host controller driver 256. The agent is capable of returning data back to the client 104. In the case where events such as interrupts need to be reported from the host controller 206 to the host controller driver 256, the packet encoder and decoder 254 receives the message from client 104 via its agent 204.

Host controller driver 256 is a driver for host controller 206. A “host controller driver” is defined throughout this specification as a driver that takes messages from other drivers in a system (for example, a mouse driver or keyboard driver) and transfers them to hardware in a manner that is consistent with the hardware's communication requirements. In some embodiments, a host controller driver is a driver that takes messages from other drivers in a system and transfers them to hardware in a manner that is not only consistent but also sufficient with the hardware's communication requirements. In some embodiments, the USB stack implementation is a mix of user mode and kernel mode components, each having different responsibilities and roles. The user mode stack is a combination of hub and host controller driver and receives notifications of changes on the USB ports. Once a device is enumerated on a USB port on the client device, the stack decides whether to handle it in the user mode or to pass it along to a kernel mode bus driver which will create a device that appears into the server system. Because the goal is to make certain HID (for example, a keyboard and mouse) attached to the client work for a non-console session on the server, the hybrid stack processes input devices locally in the user mode subsystem. If the newly connected device is anything other then an input device, it passes it along to the kernel mode driver. Handling language device and pointing device input such as keyboard and mouse input at the user level enables passing input to the session with which the user is interacting, otherwise it would pass the input to the console session, invisible to the user.

USB kernel driver 258 comprises a virtual bus driver to manage the creation and deletion of USB devices in the system. In some embodiments, the OS used is MICROSOFT WINDOWS based and because no USB controller hardware is discovered by the OS during installation, the native OS USB stack is not loaded by default. The virtual bus driver is a kernel mode driver that simulates a USB bus and manages devices that show up on that bus. In this example, the computer network acts as a bus and the driver needs to plug into the network stack in order to be able to communicate with the USB hardware and devices attached to it.

When devices are plugged into the client, the hardware relays this notification over the network to the software running on the operating system, a user mode subsystem called “PanoDAS”. The bus driver is notified of the presence of a new device. The software also provides the bus driver with information about the USB device's device, interface, and other descriptors. The bus driver can further query various other string descriptors in order to facilitate the creation of an actual device into the operating system.

The bus driver uses an Input-Output Control (“IOCTL”) interface to the PanoDAS. This is a private interface and is used by the PanoDAS to inform the bus driver of device plug and unplug notifications. This interface is also used by the bus driver to communicate with the device which includes extracting various descriptors and data transfers. PanoDAS assigns addresses to each device that it discovers and these are used by the bus driver to uniquely identify each device on the virtual bus. As part of its responsibilities, the Bus driver also handles the plug-and-play (PNP) related requests that the operating system sends down to query and set the state of the device.

The creation of a device into the system requires the bus driver to provide a hardware identifier (“ID”) and a Compatible ID for the device. In some embodiments, these are required by the MICROSOFT WINDOWS operating system to help locate a suitable driver for the device and placing the driver in the right stack.

In these embodiments using MICROSOFT WINDOWS, the Hardware ID is of format USB\\Vid_XXXX&Pid_XXXX&Rev_XXXX\0 and the Compatible ID is of format USB\\Class_(—)00&SubClass_(—)00&Prot_(—)00\0. In the Hardware ID, the Vid number is the Vendor ID of the USB device and is retrieved from the device descriptor of the device and is placed after “Vid_”, replacing the XXXX. Similarly the Pid represents the Product ID and Rev represents the Revision No. These are also retrieved from the device descriptor. Compatible ID uses Class, SubClass and Protocol information from the Interface Descriptor of the device.

The bus driver creates a Physical Device Object (“PDO”) for this device with the appropriately formed strings and re-enumerates the bus. This leads to the OS discovering the presence of a new device on the bus and it immediately locates and loads a suitable driver, if found, for this device. For example, if a USB thumb drive is plugged into thin client 104, the OS will find a match in the USBStor.sys driver and this driver will be loaded.

Once the correct driver for this device is loaded, the driver first configures and then operates the device. It does so by sending USB Request Blocks (“URBs”) and other IOCTL requests down to the PDO of the device. The URBs are used to obtain various descriptors and do data transfers to and from the device. Since the virtual bus driver owns the PDO of this USB device, it observes all of these requests coming down from the driver (UsbStor.sys in case of mass storage devices).

The bus driver parses these URBs and submits the appropriate request to the device over the network. On the other end the hardware parses these requests and submits them directly to the USB hardware. When a device is detached from the system, the hardware detects it and sends a notification. This results in the bus driver notifying the operating system and removing the PDO from the bus. The bus driver must also ensure there are no pending requests on the PDO. If any are pending, they must be finished before it can remove the device.

Hub driver 260 is the generic driver for the USB hub internal to thin client 104. The internal hub on thin client 104, which is a hub attached to external USB ports or connectors on thin client 104. In some embodiments, three external USB ports are used for thin client 104.

Language device driver 262 and pointing device driver 264 are designed to be compatible with the assistance engine 208, message analyzer 210 and hardware cursor 212 to facilitate TD resubmission or parsing pointing device cursor data. A generic driver 266 is provided for transient states to facilitate OS drivers for non-language and non-pointing devices, for example mass storage devices. Security engine 268 reciprocates with security engine 214 to allow for selective security and encryption of USB data between server 102 and thin client 104.

FIG. 3 is a flow chart illustrating an embodiment of a process for USB over a thin network. This process may be implemented between server 102 and thin client 104 from FIG. 1. In the example shown, the process starts at step 302 and ends after step 304.

In step 302, server 102 initializes the host controller 206 on thin client 104. This is required before, for example, a mouse or keyboard can be “enumerated”, meaning both detected and initialized.

In step 304, the assistance engine 208, message analyzer 210, and/or server 102 begin processing USB devices that become attached to host controller 206. These USB devices include for example, keyboard, mice and storage devices.

FIG. 4 is a flow chart illustrating an embodiment of a process for initializing a USB host controller. This process may be implemented in step 302 of FIG. 3. In the example shown, the process starts at step 402 and ends after step 408.

In step 402, server 102 issues a series of instructions to initialize the host controller 206. On thin client 104, the instructions resolve to a series of register reads and writes of the hardware host controller 206. This one-time configuration sets parameters such as width of the data bus, analog or digital overcurrent detection, and device-specific hardware configuration.

In step 404, server 102 enumerates and configures the internal USB hub at thin client 104. Server 102 sends a series of instructions to the host controller 206 that result in transactions on the USB bus. These transactions initialize the USB hub. Before this configuration takes place, server 102 and thin client 104 cannot communicate with any USB devices attached to thin client 104.

In step 406, server 102 detects that a USB device 106 has been plugged into thin client 104 and determines to configure it. In this case, the internal hub notifies the server that a device has been plugged into the thin client and the server configures it.

In step 408, server 102 issues commands to retrieve the USB device, configuration, and interface descriptors of the attached device 106. These descriptors inform server 102 of the type of device 106 attached.

FIG. 5 is a flow chart illustrating an embodiment of a process for processing USB devices using a hybrid USB stack. This process may be implemented in step 304 of FIG. 3. In the example shown, the process starts at step 502 and ends after steps 504, 508, or 512.

If it is determined at step 502 that a USB device 106 that has been plugged in during step 406 is a language device, then control is transferred to step 504; otherwise, control is transferred to step 506. In step 504, the language information is processed. For example, if a keyboard is plugged in, the keystrokes are processed. The keystrokes are then injected in a user's input stream.

If it is determined at step 506 that a USB device 106 that has been plugged in during step 406 is a pointer device, then control is transferred to step 508; otherwise, control is transferred to step 510. In step 508, the pointing information is processed. For example, if a mouse is plugged in, the cursor data is processed. The cursor data is then injected in a user's input stream.

In step 510, as the device is neither a language device nor a pointing device, it is assigned a generic driver 266 in a transient state. Device processing is passed to the virtual bus driver in USB kernel driver 258. In step 512, the virtual bus driver creates an object for the new device from server 102. The user mode retains generic driver 266 as a handle to the device.

FIG. 6 is a flow chart illustrating an embodiment of a process for processing USB language devices. For the purposes of illustration, it will be assumed that the device attached is a keyboard, but the example is generalized without limitation to any language device. This process may be implemented in step 304 of FIG. 3 and step 504 of FIG. 5. In the example shown, the process starts at step 602 and ends after step 614.

In step 602, server 102 creates a prototypical Transfer Descriptor and writes it to the host controller 206. This TD has a numerical index associated with it, “tID x”. In step 604, server 102 configures assistance engine 208, telling it that the Transfer Descriptor with tID x should be accelerated. In step 606, server 102 submits the Transfer Descriptor to the host controller 206.

If it is determined in step 608 that a key is pressed on the keyboard, then control is transferred to step 610; otherwise control continues to wait at step 608. In step 610, the host controller 206 signals (via an interrupt) assistance engine 208 that data is available. Assistance engine 208 reads the data from the host controller 206 and sends the data to server 102. Server 102 processes the data and sends it up through the software stack to the OS.

In step 612, assistance engine 208 uses the completed Transfer Descriptor along with the Prototypical Transfer Descriptor and a collection of fixed transformation rules to submit a modified Transfer Descriptor to the host controller 206. This step happens without intervention from server 102.

In step 614, if an error occurs in any transfer, assistance engine 208 transfers the error result to server 102 and does not automatically submit a new Transfer Descriptor. Server 102 handles the error, which may involve restarting the automatic submission beginning with step 602 above. The removal of the keyboard from the bus appears as an error that would not result in a restart.

FIG. 7 is a flow chart illustrating an embodiment of a process for USB information extraction. For the purposes of illustration, it will be assumed that the device attached is a mouse, but the example is generalized without limitation to any pointing device. This process may be implemented in step 304 of FIG. 3 and step 508 of FIG. 5. In the example shown, the process starts at step 702 and ends after step 722.

In step 702, server 102 reads the mouse's Human Interface Device (HID) descriptor. This descriptor includes information on how the data sent from the mouse are formatted.

In step 704, server 102 parses the HID descriptor and configures message analyzer 210 with information including the location of the spatial coordinates such as x and y coordinates, and event data, such as scroll wheel and button data, within a specific HID report.

In step 706, server 102 initializes data transfer between the pointing device and the client. Server 102 first creates a prototypical Transfer Descriptor and writes it to the host controller 206. This TD has a numerical index associated with it, “tID x”. Server 102 then configures assistance engine 208, telling it that the Transfer Descriptor with tID x should be accelerated. Server 102 finally submits the Transfer Descriptor to the host controller 206. Mouse processing leverages TD acceleration.

If it is determined in step 708 that a the mouse was moved or one of its buttons or scroll wheel is clicked, then control is transferred to step 710; otherwise control continues to wait at step 708. In step 710, the host controller 206 signals (via an interrupt) assistance engine 208 that data is available. Assistance engine 208 parses the data and verifies that it contains the configured report ID.

If it is determined in step 712 that the data contains the configured report ID, control is transferred to step 714; otherwise control is transferred to step 720. In step 714, message analyzer 210 parses the report and extracts the change in spatial data, for example x and y coordinate, as well as information on event data, for example the scroll wheel and button state. Hardware cursor 212 is updated to reflect the internal position of the pointer and renders the screen display with a new representation of the pointer.

In step 716, if the mouse button has changed state from the previous report, message analyzer 210 immediately sends the current mouse position and button state to server 102. Otherwise, it determines if the configured time since the last position update has elapsed and may send the update to server 102. The message to server 102 is the absolute position of the cursor: the result of all the mouse movement message analyzer 210 has received. The position updates are the same for all mice and their format is independent of the format of the USB mouse data.

In step 718, assistance engine 208 uses the completed Transfer Descriptor along with the Prototypical Transfer Descriptor and a collection of fixed transformation rules to submit a modified Transfer Descriptor to the host controller 206. This step happens without intervention from server 102.

In step 720, message analyzer 210 does not attempt to parse the data. Rather, the host controller 206 first signals (via an interrupt) assistance engine 208 that data is available. Assistance engine 208 reads the data from the host controller 206 and sends the data to server 102. Server 102 processes the data and sends it up through the software stack to the OS. Assistance engine 208 then uses the completed Transfer Descriptor along with the Prototypical Transfer Descriptor and a collection of fixed transformation rules to submit a modified Transfer Descriptor to the host controller 206. This step happens without intervention from server 102.

In step 722, if an error occurs in any transfer, assistance engine 208 transfers the error result to server 102 and does not automatically submit a new Transfer Descriptor. Server 102 handles the error, which may involve restarting the automatic submission beginning with step 602 above. The removal of the mouse from the bus appears as an error that would not result in a restart.

FIG. 8A and FIG. 8B are an example of a register map for an assistance engine and message analyzer. The registers for assistance engine 208 and message analyzer 210 may be stored within their respective systems or elsewhere in thin client 202.

Register 802 is an example of a PTD acceleration enable register, where a bit could be asserted to enable PTD acceleration for a given PTD ID. Register 804 is an example of a USB pointing device acceleration enable register, where a bit could be asserted to enable the pointing device acceleration for a plurality of pointing devices, in this example two mice. The register also allows HID report IDs that do not match the configured device report ID to be sent to the host as PTD accelerated completions or silently dropped to reduce power consumption or network bandwidth.

Register 806 is an example of a ID register for a plurality of pointing devices, in this example two mice. The register stores for each pointing device channels the report ID and the mouse PTD. Register 808 is an example of a scale register for a plurality of pointing devices, in this example two mice. Pointing device scaling allows for pointing device motion acceleration by scaling the “delta” or raw pointing device velocity by a multiplier shifted by a specified number of bits. Register 810 is an example of a frequency register for a plurality of pointing devices, in this example two mice. The frequency register controls how often messages are sent from message analyzer 210 to server 102, and controls merging of a plurality of messages to reduce bandwidth between thin client 104 and server 102.

Register 852 is an example of a register to store a spatial message for one dimension for a plurality of pointing devices, for example the X position message for two mice. Other examples include registers for Y position messages and Z position messages.

Register 854 is an example of a register to store an event message for one type of event for a plurality of pointing devices, for example the first button message for two mice. Other examples include registers for second, third and fourth button messages or scroll wheel button messages.

Register 856 is an example of a register to store the maximum coordinates for the screen extents for hardware cursor 212. Register 858 is an example of a register to store the minimum coordinates for the screen extents for hardware cursor 212. Register 860 is an example of a register to store the hotspot for hardware cursor 212.

FIG. 9 is a flow chart illustrating an embodiment of a process for USB selective encryption. This process may be implemented in security engine 214 of FIG. 2A and security engine 268 of FIG. 2B. In the example shown, the process starts at step 902 and ends after step 910.

In step 902, host controller 206 determines an identifying message by performing a host controller service for the USB device 106, for example the completion of a particular TD. In step 904, the host controller 206 transmits the identifying message to a server, for example the security engine 268. In step 906 the security engine 268 identifies the USB device 106 and state based at least in part on the identifying message, for example whether it is a mouse, or whether it is a keyboard and the keyboard user is entering a password. In some embodiments only the USB device 106 is identified and the state is not identified.

In step 908, the security engine 268 determines the security policy for the USB device 106 and state, and transmits an indication of the security policy back to security engine 214 for selectively implementing the security policy on USB device 106. In some embodiments, the state if any is ignored. In some embodiments, nothing is transmitted to the client if no further security action is necessary. In step 910, the client then regards the security policy and configures the host controller service. In some embodiments the security policy is to encrypt USB data traffic between thin client 104 and server 102. In some embodiments, encryption uses an appropriate key exchange algorithm like RSA, and an encryption algorithm like AES-128 to encrypt the data.

FIG. 10 is an example of a register map for a security engine. The registers for security engine 214 may be stored within its respective system or elsewhere in thin client 202.

Register 1002 is an example of a register to flag whether a particular isochronous USB transfer is to be encrypted. Register 1004 is an example of a register to flag whether a particular interrupt USB transfer is to be encrypted. Register 1006 is an example of a register to flag whether a particular bulk or Asynchronous Transfer List (“ATL”) USB transfer is to be encrypted. Register 1008 is an example of a register to select when access of registers and memory space of the host controller 206 is to be encrypted. Access to or from register and memory space larger that the contents of the example register need to be encrypted.

Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive. 

What is claimed is:
 1. A server configured to interact with a remote USB device comprising: an interface to receive an identifying message from a remote client associated with the remote USB device to a security policy engine, wherein the identifying message includes a USB transfer descriptor associated with the remote USB device; the security policy engine, configured to: identify the remote USB device based at least in part on the USB transfer descriptor provided in the received identifying message; and determine a security policy for the remote USB device based at least in part on the identity of the remote USB device; and the interface, further configured to transmit a policy message comprising the determined security policy from the security policy engine to the remote client, wherein USB data traffic between the remote client and the server is selectively encrypted by the remote client based at least in part on the security policy, wherein the server transmits an instruction comprising a set of parameters which includes at least one of a width of a data bus, an analog or digital overcurrent detection, and a device-specific hardware configuration, to a host controller of the remote client for initializing the host controller before the remote USB device is detected, and wherein the security policy engine is a hardware processor.
 2. A server as recited in claim 1, wherein the security policy is refined on a transaction by transaction basis.
 3. A server as recited in claim 1, wherein the security policy includes a policy to determine which messages to encrypt.
 4. A server as recited in claim 1, wherein the security policy includes a policy to determine which unencrypted messages to reject.
 5. A server as recited in claim 1, wherein the security policy includes an encryption scheme.
 6. A server as recited in claim 1, wherein the security policy includes a public key encryption scheme.
 7. A server as recited in claim 1, wherein the security policy includes a symmetric key encryption scheme.
 8. A server as recited in claim 1, wherein the policy message selectively implements the security policy for a remote USB device with a specified transfer descriptor index.
 9. A server as recited in claim 1, wherein the interface is further configured to selectively not implement the security policy on the remote USB device.
 10. A server as recited in claim 1, wherein the security policy is selectively not implemented for a USB configuration of the remote USB device.
 11. A server as recited in claim 1, wherein the remote USB device includes a keyboard.
 12. A server as recited in claim 1, wherein the remote USB device includes a keyboard and wherein the security policy is selectively not implemented for a keyboard configuration for predetermination of extracted information of a keyboard transfer descriptor.
 13. A server as recited in claim 1, wherein the remote USB device includes a mass storage device.
 14. A server as recited in claim 1, wherein the remote USB device includes a mass storage device, and wherein the security policy is selectively implemented for a subset of files on the mass storage device.
 15. A server as recited in claim 1, wherein the remote USB device includes a mass storage device, and wherein the security policy is selectively not implemented for a subset of directories on the mass storage device.
 16. A server as recited in claim 1, wherein the remote USB device includes a mass storage device, and wherein the security policy is selectively not implemented for a subset of operations on the mass storage device.
 17. The server as recited in claim 1, wherein the security policy engine selects the security policy from at least two security policies based on a type of the USB transfer descriptor.
 18. The server as recited in claim 1, wherein the security policy engine further identifies a state of the remote USB device based on the received identifying message and wherein the security policy engine selects the security policy from at least two security policies further based on the identified state of the remote USB device.
 19. The server as recited in claim 1, wherein the security policy identifies type of access to encrypt for the same remote USB device such that a first transaction between the remote server and the remote client, which is a first type of access, is encrypted and a second transaction between the same remote server and the same remote client, which is a second type of access different from the first type of access, is not encrypted.
 20. The server as recited in claim 1, wherein prior to the host controller detecting the remote USB device, the server transmits a series of instructions to the host controller for initializing a USB bus to which the remote USB device can be connected.
 21. The server as recited in claim 1, wherein the security policy comprises identifying memory space access to which is to be encrypted and a particular type of USB transfer to be encrypted.
 22. A client configured to interact with a local USB device comprising: a host controller, coupled to the local USB device, configured to be initialized upon receiving an instruction comprising a set of parameters which includes at least one of a width of a data bus, an analog or digital overcurrent detection, and a device-specific hardware configuration from a server before the local USB device is detected; a security policy engine, coupled to the host controller; an interface, configured to: send an identifying message to the server, the identifying message includes a USB transfer descriptor associated with the local USB device; and receive a policy message comprising a security policy from the server, the security policy being determined by the server based on the USB transfer descriptor; wherein the security policy engine is configured to: regard the policy message and configure the host controller; and selectively encrypt USB data traffic between the remote client and the server based at least in part on the security policy.
 23. A client as recited in claim 22, wherein the host controller includes a memory protected by the security policy.
 24. A client as recited in claim 22, wherein the host controller includes a memory protected by the security policy based on the memory address.
 25. A client as recited in claim 22, wherein the security policy is refined on a transaction by transaction basis.
 26. A client as recited in claim 22, wherein the security policy includes a policy to determine which messages to encrypt.
 27. A client as recited in claim 22, wherein the security policy includes a policy to determine which unencrypted messages to reject.
 28. A client as recited in claim 22, wherein the security policy includes an encryption scheme.
 29. A client as recited in claim 22, wherein the security policy includes a public key encryption scheme.
 30. A client as recited in claim 22, wherein the security policy includes a symmetric key encryption scheme.
 31. A client as recited in claim 22, wherein the policy message selectively implements the security policy for the local USB device with a specified transfer descriptor index.
 32. A client as recited in claim 22, wherein the security policy is selectively not implemented for a USB configuration of the local USB device.
 33. A client as recited in claim 22, wherein the local USB device includes a keyboard.
 34. A client as recited in claim 22, wherein the local USB device includes a keyboard and wherein the security policy is selectively not implemented for a keyboard configuration for predetermination of extracted information of a keyboard transfer descriptor.
 35. A client as recited in claim 22, wherein the local USB device includes a mass storage device.
 36. A client as recited in claim 22, wherein the local USB device includes a mass storage device, and wherein the security policy is selectively implemented for a subset of files on the mass storage device.
 37. A client as recited in claim 22, wherein the local USB device includes a mass storage device, and wherein the security policy is selectively not implemented for a subset of directories on the mass storage device.
 38. A client as recited in claim 22, wherein the local USB device includes a mass storage device, and wherein the security policy is selectively not implemented for a subset of operations on the mass storage device.
 39. A client as recited in claim 22, wherein the security policy engine configures the host controller to interact with the local USB device if and only if the local USB device regards the security policy and otherwise reject interaction.
 40. A method to interact with a remote USB device comprising: receiving an identifying message from a remote client associated with the remote USB device, wherein the identifying message includes a USB transfer descriptor associated with the remote USB device; identifying the remote USB device based at least in part on the USB transfer descriptor provided in the received identifying message; determining a security policy for the remote USB device based at least in part on the identity of the remote USB device; and transmitting a policy message comprising the determined security policy to the remote client wherein USB data traffic between the remote client and a server is selectively encrypted by the remote client based at least in part on the security policy, and wherein the server transmits an instruction comprising a set of parameters which includes at least one of a width of a data bus, an analog or digital overcurrent detection, and a device-specific hardware configuration, to a host controller of the remote client for initializing the host controller before the remote USB device is detected.
 41. A method to interact with a local USB device comprising: initializing a host controller upon receiving an instruction comprising a set of parameters which includes at least one of a width of a data bus, an analog or digital overcurrent detection, and a device-specific hardware configuration, from a server before the local USB device is detected; determining an identifying message by performing a host controller service for the local USB device, wherein the identifying message includes a USB transfer descriptor associated with the local USB device; transmitting the identifying message to a server; receiving a policy message comprising a security policy from the server, the security policy being determined by the server based on the USB transfer descriptor; and configuring the host controller service; and selectively encrypting USB data traffic to and from the server based at least in part on the security policy.
 42. A server configured to interact with a remote USB device comprising: an interface to receive an identifying message from a remote client associated with the remote USB device to a security policy engine, wherein the identifying message includes a USB transfer descriptor associated with the remote USB device; the security policy engine, configured to: identify the remote USB device based at least in part on the USB transfer descriptor provided in the received identifying message; and determine a security policy for the remote USB device based at least in part on the identity of the remote USB device; and the interface, further configured to transmit a policy message comprising the determined security policy from the security policy engine to the remote client, wherein the remote client is configured to: implement the received security policy on the remote USB device; and selectively encrypt USB data traffic from the remote client to the server based at least in part on the security policy, wherein the security policy engine determines the security policy from among at least two security policies, wherein the at least two security policies comprise a plurality of stored registers comprising: a first register to flag whether a particular isochronous USB transfer is to be encrypted; a second register to flag whether a particular interrupt USB transfer is to be encrypted; a third register to flag whether a particular bulk or Asynchronous Transfer List is to be encrypted; and a fourth register to select when access of registers and memory space of the remote client is to be encrypted, and wherein the security policy further comprises type of access to be protected, and wherein the security policy engine is a hardware processor. 